Glazing unit

ABSTRACT

A glazing unit comprising a sheet of glass having a coating consisting essentially of silicon on a major face thereof, and a frame for that sheet.

This is a division of Application Ser. No. 585,522, filed June 10, 1975now U.S. Pat. No. 4,019,887.

BACKGROUND OF THE INVENTION

This invention relates to the coating of glass and in particular to amethod for the coating of glass with silicon, and to silicon-coatedglass, in particular flat glass having a uniform coating comprisingelemental silicon on one or both surfaces. The invention further relatesto apparatus for coating glass constructed to supply coating material ingaseous form to the vicinity of a glass surface to be coated.

A variety of coating materials have been used or have been proposed formodifying the radiation transmission and reflection characteristics ofglass, for enhancing the appearance of glass, or for providingdecorative patterns on a glass surface. Such coatings often serve morethan one purpose. For example, metal oxide coatings andvacuum-evaporated metal coatings have been used to endow glass withsolar control properties while at the same time giving the glass anattractive hue.

It is known that silanes decompose on heating to produce silicon. Thussilanes have been used as a source for the production of silicon for usein electro-conductive devices.

It is a main object of the present invention to provide a coating forglass which can be applied economically, has good solar controlproperties, and a pleasing appearance, to add to the range of solarcontrol coated glass already available, particularly for window glazingapplications.

The invention is based on the discovery that a silicon coating can beformed on a hot glass surface, for example on a continuous ribbon of hotglass, by an economical process which provides a durable and uniformcoating with desirable solar control properties and a pleasing anduniform appearance.

SUMMARY

The invention provides a method of coating glass in which the glass ismoved past a coating station while the temperature of the glass is atleast 400° C. Silane-containing gas is supplied to the coating station,and is released close to the glass surface at a substantially constantpressure across the glass surface into a hot zone opening towards andextending across the glass surface. Non-oxidising conditions aremaintained in said hot zone. A coating consisting of or includingsilicon is produced on the glass by pyrolysis of the gas.

The composition of the gas may be regulated to maintain a rate of silanepyrolysis on the hot glass surface producing a silicon coating ofpredetermined thickness on that surface.

Usually the gas flow rate is regulated to obtain a uniform coating andthe silane concentration in the gas is regulated to provide the desiredcoating thickness.

The temperature of the glass surface should be above 400° C. in order todecompose the silane on that surface, but may be considerably higher,for example up to 750° C.

However, the use of high temperatures may result in distortion in thecoated glass and tends to produce a coated glass haing an opalescent orhazy surface appearance. We prefer to use a temperature below 700° C.,preferably in the range 500° C. to 700° C., unless distortion and/orhaziness in the coated product is acceptable.

The method of the invention may be employed for coating a surface of aribbon of glass advancing past the coating station, and the compositionof the gas is regulated in relation to the speed of advance of theribbon.

For coating a ribbon of glass which is being advanced along a bath ofmolten metal over which a protective atmosphere is maintained, thesilane-containing gas is preferably released into the hot zone which islocated where the glass temperature is in the range 600° C. to 670° C.

The method of the invention enables a uniform coating of silicon ofdesired thickness to be produced on a moving glass surface by control ofthe process conditions. In practice, when treating a newly-producedribbon of glass on line, the rate of movement of glass past the coatingstation is generally dictated by glass-making considerations. We havefound that a convenient procedure for producing a uniform coating ofdesired thickness is to adjust the gas flow rate until a uniform coatingis obtained and then to adjust the concentration of silane in the gasuntil the desired thickness of coating is obtained. However, thethickness may be controlled in other ways. For example, the temperatureof the glass may be increased to increase the thickness of the coatingproduced. When treating a moving ribbon of glass on-line in theproduction process this may involve moving the coating station along theribbon. It will be appreciated that this is not always convenient.

A silicon coating may also be applied by the method of the invention toeither or both surfaces of a ribbon of glass which is being annealed andthe method also provides for the coating of a ribbon of glass which isadvancing through an annealing lehr, the silane-containing gas beingreleased into a hot zone which is located in the lehr where the glasstemperature is in the range 400° to 700° C.

Thus the process of the invention is applicable to the treatment ofrolled plate glass in the lehr. When treating rolled plate glass, hazeor distortion in the final product may be acceptable and it maytherefore be possible to work at temperatures above 700° C., for exampletemperatures of about 750° C. The method of the invention may also beused for the on-line treatment of sheet glass.

The silane in the gas which is flowing towards and in the vicinity ofthe hot glass surface being coated becomes preheated before it reachesthat surface. It is desirable that the temperature of the silane gaswhen it contacts the glass surface being coated should be as hot as isconsistent with avoiding decomposition in the gaseous phase. Thesilane-containing gas supplied to the coating station is maintained at atemperature at which no significant decomposition occurs, certainlybelow 400° C., until it is being released into the immediate vicinity ofthe hot glass surface.

The method of the invention is especially applicable for the depositionof coatings consisting essentially of silicon, but it may also be usedfor the deposition of coatings containing silicon and other materials.Thus, for example, the silane-containing gas may also contain gaseousprecursors for other coating materials, which may or may not react withsilicon deposited from the silane. The method of the invention may beused to apply coatings to clear glass or coloured glass, for example,the brown, grey or green body-coloured glasses which are commerciallyavailable.

Preferably the silane-containing gas comprises from 0.1% to 20% byvolume of silane, up to 10% by volume of hydrogen, and from 70% to 99.9%by volume of inert gas. The silane may be monosilane (SiH4).

Further the invention provides apparatus for coating glass comprising agas distributor for locating transversely of the path of travel of aglass surface to be coated, including a gas supply duct for supplyingcoating material in gaseous form, means for controlling the temperatureof the duct, and an elongated open-faced chamber for positioningadjacent said path and communicating along its length with the gassupply duct through gas-flow restrictor means arranged to provide gasrelease from the duct into the chamber at a constant pressure along thelength of the chamber.

The means for controlling the temperature of the duct may be means forcooling the duct.

The apparatus of the invention is especially suitable for producing asilicon coating from a silane-containing gas, but it may also be usedfor the production of other coatings by deposition from the gas phase.

The gas-flow restrictor means may be constituted by an array of smallcross-sectional area channels leading from the gas supply duct to thechamber, the dimensions of which channels are selected so that thepressure drop along the duct is small compared to the pressure dropalong the channels.

Thermal insulation may be provided between the duct and the chamber. Byprovision of thermal insulation, the gas supply duct and the gas-flowrestrictor means may be kept cool to avoid decomposition of the silanein the gaseous phase in the duct or on the restrictor while the gas israpidly heated in the chamber prior to its contact with the glasssurface after its release into that chamber at a constant pressure alongthe length of the chamber. Moreover the provision of thermal insulationlimits the cooling of the walls defining the chamber by means coolingthe duct and permits improved control of the conditions in the chamber.

Such apparatus may be used, for example to provide a uniform siliconcoating on a ribbon of float glass 3 m wide.

The side walls of the chamber may be shaped to define a channel in thechamber diverging from the restrictor means to the open face of thechamber.

The provision of shaped side walls for the chamber controls the gas flowpattern within the chamber. The gas flow pattern is also dependent uponother parameters such as the temperature of the glass surface, thetemperature of the silane-containing gas released into the chamber, andthe speed of the glass surface past the open face of the chamber. Bycontrolling the various parameters, the gas flow pattern can becontrolled to achieve uniform coatings and effective silane usage whilesubstantially avoiding silane decomposition in the gaseous phase.

When using silane to apply a silicon coating to a ribbon of glassadvancing along a molten metal bath, the temperature of the gas supplyduct should be controlled so that the silane-containing gas ismaintained at a temperature well below 400° C. before it flows throughthe gas-flow restrictor means into the outlet chamber. The means forcontrolling the temperature of the duct may comprise a jacket forheating or cooling fluid in thermal contact with the gas supply duct. Tocool the duct, water may be circulated through the jacket to maintainthe gas at about the temperature of the cooling water. Cooling of thedistributor also serves to alleviate bowing of the distributor andsetting-up problems which arise from such bowing.

The invention provides a method of forming on a hot ribbon of glass, auniform and durable silicon coating which endows the glass withdesirable solar control properties and a pleasing appearance. Thus theinvention also provides, as new products, a ribbon of glass having asubstantially uniform cooling comprising elemental silicon thereon, andpieces of coated glass cut from the ribbon. The coating may consistessentially of silicon.

The coating may have a thickness of 250A to 600A determined as hereindescribed. Further the coating may have a thickness in the range 300A to450A determined as herein described.

Further the invention comprehends a glazing unit comprising a sheet ofglass having a coating containing elemental silicon on a major surfacethereof, and a frame for that sheet. When the sheet is directly glazedin a wall, the frame is constituted by the edges of the wallssurrounding the sheet.

The coating may have a thickness in the range 250A to 600A determined asherein described. The thickness of the coating may be in the range 300Ato 450A.

The invention also includes a multiple-glazing unit comprising at leasttwo sheets of glazing material in parallel spaced relationship, at leastone sheet being a sheet of glass having a coating comprising elementalsilicon thereon. The silicon coating may be disposed internally of theunit, but not necessarily so.

The invention further provides silicon-coated flat glass having auniform silicon coating of optical thickness in the range 950A to 1600Aand a refractive index in the range 3.0 to 4.0. Such silicon coatings,when coated on clear glass, typically provide a coated glass having,when viewed from the coated side, a white light transmission in therange 17% to 34%, (determined using a C.I.E. Illuminant C source) adirect solar heat transmission in the range 27% to 45% and a solarradiant reflection in the range 34% to 52%.

The invention also comprehends flat glass having a coating comprisingsilicon thereon whenever produced by the method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 is a vertical section through float glass manufacturing apparatusshowing a tank structure containing a molten metal bath and a gasdistributor according to the invention located transversely of the pathof travel of the ribbon of glass near the outlet end of the apparatus,

FIG. 2 is a section on line II--II of FIG. 1,

FIG. 3 is a section on line III--III of FIG. 2 showing more detail ofthe gas distributor,

FIG. 4 is an underneath view of the distributor of FIG. 3 showinggas-flow restrictor means through which cooled gas is released into alower open-faced chamber,

FIG. 5 is an enlargement of part of the gas-flow restrictor means,

FIG. 6 is a view in elevation in the direction of arrow VI of FIG. 3showing a mechanism to adjust carbon side pieces on the distributor,

FIG. 7 is a part-section similar to FIG. 3 which illustrates amodification of the gas distributor with shaped side walls for theopen-faced chamber providing a diverging shape to that chamber,

FIG. 8 is a part-section similar to FIG. 7 which illustrates yet anotherform of shaped side walls for the open-faced chamber of the distributor,

FIG. 9 is a section similar to FIG. 3 of an alternative form of gasdistributor with yet another form of open-faced chamber,

FIG. 10 is a diagrammatic cross-section through another embodiment ofthe invention for coating glass in an annealing lehr,

FIG. 11 is a cross-section through a glazing unit according to theinvention having a single sheet of silicon-coated glass mounted in aframe, and

FIG. 12 is a cross-section through a multiple glazing unit according tothe invention.

In the drawings the same references indicate the same or similar parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 6 illustrate a preferred form of apparatus according to theinvention for use in applying a uniform thin coating of silicon to theupper surface of a ribbon of float glass. The coating is applied towardsthe outlet end of the bath as the ribbon approaches the location whereit is lifted from the surface of a bath of molten metal on which theribbon has been formed.

FIGS. 1 and 2 illustrate molten glass 1 being delivered in conventionalmanner along a canal 2 leading from the forehearth of a glass meltingfurnace. The canal 2 terminates in a spout having side jambs 3 and a lip4 and flow of molten glass to the spout, usually soda-lime-silica glass,is controlled by a regulating tweel 5. The spout extends over the inletend wall 6 of a tank structure comprising a floor 7, an outlet end wall8 and side walls 9. The tank structure contains the bath of molten metal10, usually molten tin or tin alloy in which tin predominates, andmolten glass flows as indicated at 11 over the spout lip 4 onto thesurface of the molten metal bath 10 at the inlet end of the bath wherethe temperature is maintained in the region of 1,000° C. by heaters,indicated at 12, mounted in a roof structure 13 which is supported overthe tank structure and defines a head space 14 above the molten metalbath. The roof structure has an inlet end wall 15 which dependsdownwardly close to the surface of the molten metal bath 10 at the inletend of the bath to provide an inlet 16 of restricted height. Anextension 17 of the roof structure extends up to the tweel 7 to providea chamber in which the spout is enclosed.

The roof structure also has a downwardly depending wall 19 at the outletend. An outlet 20 for a ribbon of glass 21 produced on the bath isdefined between the lower face of the outlet end wall 19 of the roofstructure and the upper face of the outlet end wall 8 of the bath.Driven traction rollers 22 are mounted beyond the outlet 20 with theupper surfaces of the rollers just above the level of the upper surfaceof the bath end wall 8 so that the ribbon of glass is lifted gently fromthe bath surface for discharge horizontally away from the outlet 20 fromthe bath on the rollers 22.

A protective atmosphere, for example 95% nitrogen and 5% hydrogen, ismaintained at a plenum in the head space 14 over the bath, beingsupplied through ducts 23 extending downwardly through the roof 13 andconnected to a common header 24. Protective atmosphere flows outwardlythrough the inlet 16 to fill the chamber 17 enclosing the spout. Atemperature gradient is maintained down the bath from a temperature ofabout 1,000° C. at the inlet end of the bath to a temperature in therange about 570° C. to 650° C. at the outlet end where the ribbon ofglass is discharged from the bath. At this lower temperature the glassis sufficiently stiffened to be unharmed by its contact with thetraction rollers 22 but can still be lifted from the bath surface asillustrated.

The molten glass 11 which flows over the spout lip 3 onto the bath ispermitted to flow laterally on the bath as illustrated in FIG. 2 to forma layer 25 of molten glass which is then advanced as a ribbon 21 whichis cooled and discharged from the bath. The width of the tank structurecontaining the bath between the side walls 9 is greater than the widthof the ribbon.

A gas distributor for supplying silane-containing gas to the surface ofthe glass ribbon is located transversely of the path of travel of theribbon of glass along the bath near the outlet end of the bath asillustrated in FIGS. 1 and 2 where the temperature of the glass is inthe range 570° C. to 670° C.

In operation of the invention there is fed to the glass surface asilane-containing gas which comprises from 0.1% to 20% by volume ofsilane, up to 10% by volume of hydrogen, and from 70% to 99.9% by volumeof inert gas, usually nitrogen. At temperatures within the range 570° C.to 670° C. the silane in the gas readily decomposes by pyrolysis on thehot glass surface leaving a deposit of silicon Si on the glass surface.Preferably the silane is monosilane SiH₄.

The gas distributor is indicated generally by the reference 26 in FIG. 1and is illustrated in more detail in FIGS. 3 to 6. The distributorcomprises a hollow channel section 27 which is welded at 28 to the roof29 of a larger inverted U-section channel member which also has sidewalls 30. The hollow channel section 27 serves as a duct 31 for thepassage of cooling fluid, usually water.

Horizontal members 32 extend inwardly from each of the side walls 30along the whole length of those side walls and the inner edges of themembers 32 define between them an elongate slot-shaped aperture 33.

Another inverted U-section member 34 is fitted symmetrically on to thehorizontal members 32 covering the aperture 33. The lower edges of themember 34 are welded to the horizontal members 32 and the member 34defines a gas supply duct 35 with the outlet aperture 33 in its lowerface.

Between the member 34 and the member 29, 30 there is defined a furtherchannel 36 of inverted U-shape for flow of cooling water.

The distributor also defines an elongate open-faced chamber 40 forpositioning adjacent the path of travel of the upper surface 41 of theribbon of glass 21 and communicating along its length with the gassupply duct 35.

In the embodiment of FIGS. 1 to 6 the open-faced chamber has a roofdefined by slabs 42 of compressed mineral fibre thermal insulationmaterial which define between them an elongate aperture 43 which isaligned with the aperture 33 in the floor of the gas supply duct 35. Theends of the chamber 40 are closed by carbon end walls 44, and each sidewall of the chamber 40 is formed by two carbon slabs 45 which areconnected together by a central pivot 46, FIG. 2, which is fixed to theside wall 30 of the duct 36.

The slabs 45 are held in position against insulating pads 47 of the samematerial as the slabs 42 which abut fixing plates 48 welded to the sidewalls 30, by bolts 49 which pass through slots 50 in the slabs and arefixed into the plates 48. A pressure spring 51 is held on each of thebolts 50 by nuts 52 and bears against an eye plate 53 on the outer faceof the slab. This arrangement permits adjustment of the slabs 45 in themanner to be described so that the bottom faces 54 of the slabs areset-up as closely adjacent the upper surface of the ribbon of glass aspossible across the whole width of the ribbon.

Gas-flow restrictor means is fixed between the apertures 33 and 43 andcomprises support plates 55 which carry a central waffle plate 56 madeup of crimped metal sheets. The support plates 55 are bolted to thehorizontal members 32 by bolts 57 whose heads are countersunk into theplates 55 and are covered by the insulating slabs 42 which are securedby a suitable adhesive to the plates 55. The central waffle plate 56comprises, as illustrated in detail in FIG. 5, a plurality of crimpedmetal strips 58 arranged "out-of-phase" to define a plurality ofchannels 59 which are of small cross-sectional area relative to thecross-sectional area of the gas supply duct 35 so that whensilane-containing gas is supplied under pressure to the duct 35 throughgas supply ducts 60 at either end of the distributor as illustrated inFIG. 2, the pressure drop along the duct 35 is small compared with thepressure drop through the restricted channels 59 and the waffle plate 56effectively constitutes gas-flow restrictor means to ensure release ofcool silane-containing gas into the outlet chamber 40 at a substantiallyconstant pressure and temperature along the whole length of the outletchamber.

The support plates 55 in which the waffle plate 56 is mounted are alsoof metal which is in intimate contact with the cooled horizontal members32 so that the waffle plate 56 is kept at a temperature below 400° C.despite the fact that the distributor is located within the headspace atthe outlet end of the float glass manufacturing apparatus where theambient temperature is slightly below the ribbon temperature.

It is desirable however that the outlet chamber 40 shall be heated byradiation from the upper surface 41 of the ribbon of glass 21 which ispassing beneath the open face of the outlet chamber, the distributorbeing so located, as illustrated in FIG. 3, that the lower edge 61 ofthe outlet chamber is located closely adjacent the upper surface 41 ofthe ribbon 21 which is to receive a silicon coating.

The provision of the thermally insulating slabs 42 ensures that the gassupply duct 35 and the waffle plate 56 can be maintained at atemperature below 400° C. so that silane does not decompose to depositsilicon either on the inner surface of the duct 35 or on the waffleplate 56. The carbon walls of the chamber 40 are maintainedsubstantially at the ambient temperature so that the space within thechamber 40 constitutes a heating zone into which cooledsilane-containing gas is released at a substantially constanttemperature and pressure across the glass surface.

Cooling water is supplied to one end of the gas distributor, outside thetank structure, as illustrated in FIG. 2. A water supply pipe 62 isconnected to the duct 36 and water flows along the duct 36 to the otherend of the distributor and then through a hole, not shown, in the roof29 and in the floor of the hollow channel section 27 into the upper duct31 within the member 27. The water flows along the duct 31 to adischarge pipe 63 at the same end of the distributor as the water supplypipe 62.

The supply of cooling water in this way cools the members 27, 29, 30 and34 so that rigidity of the gas distributor is preserved and thesilane-containing gas flowing through the gas duct 35 is kept at aboutthe temperature of the cooling water say 40° C. to 50° C.

FIG. 2 shows how the chamber 40 at the bottom of the gas distributor islocated only in a central part of the distributor and is as long as thewidest ribbon to be coated during its advance along the bath. Theaperture 33 therefore extends only over a central part of the gas supplyduct 35 and towards both ends of the duct, that is beyond the chamber 40the gas supply duct 35 and the cooling water duct 36 have a continuousfloor constituted by a continuous plate which is welded to the sidewalls 30.

The gas distributor is adjustably supported in the tank structure in themanner illustrated in FIG. 2 and is sealed into apertures 64 in the sidewalls 9 of the tank structure. For setting-up of the gas distributor theapertures 64 are unsealed and the gas distributor is run across the tankstructure from one side which is the left-hand side as illustrated inFIG. 2. The left-hand side of the distributor is held in a collar 65which is mounted on a swivel on the upper end of a threaded support rod66 the lower end of which engages a worm gear in a housing 67, whichgear is manually rotatable by a wheel 68. The housing 67 is carried on abeam trolley 69 which runs on a beam leading track 70 only a shortlength of which is shown. A loading roller 71 mounted at the upper endof a support 72 is vertically adjustable so as to provide support forthe distributor as it is run-in from the left-hand side of the tankstructure.

The distributor is guided across the tank structure on to a similarloading roller 71¹ which is mounted on the upper end of an adjustablesupport 73. The right-hand end of the distributor is run through acollar 74 which is similarly mounted to the collar 65 on a threaded rod75 engaging with a worm gear in a housing 76 which worm gear is manuallyadjustable by a wheel 77. The housing 76 is mounted on a fixed support78.

In setting-up the distributor when it has been run right through thetank structure and is secured between the collars 65 and 74, the wheels68 and 77 are rotated to lift the distributor from the loading rollers71, 71¹. Rotation of the wheels 68 and 78 also permits adjustment tolevel up the distributor across the tank structure so that the lowerfaces 54 of the side walls 45 are set-up as closely adjacent the uppersurface of the ribbon of glass as possible. In practice it is preferredto support the distributor on its back whilst it is run through the tankstructure. In this case, the distributor is put in upside down andsubsequently inverted by rotation of the collars 65 and 74 through 180°.

Despite the cooling of the members 27, 29 and 30 which helps to preserverigidity there is a certain bowing of the distributor and to compensatefor this the slabs 45 are adjustable about their central pivots 46. Thisadjustment is carried out by a mechanism illustrated diagrammatically inFIG. 2 and in more detail in FIGS. 3 and 6.

Each of the slabs 45 has five slots 50 through which the spring loadedholding bolts 49 pass. Adjacent the outer end of each slab, near to thesecond of the slots, an adjustor is fixed to the upper surface of eachof the slabs to pivot the slabs about their fixed central pivot 46within the limits of adjustment permitted by the slots 50. Generally theslabs 45 are pivoted slightly downwardly about their central pivot 46 inorder to compensate for bowing of the members 27, 29 and 30 and to bringthe lower faces 54 of the side walls as near as possible to the uppersurface of the ribbon across the whole width of the ribbon. Each of theadjustors comprises a metal foot plate 79 which is fixed by bolts 80 tothe upper surface of its slab 45. The foot plate carries an upstandinglug 81 to which a fork 82 on the lower end of a threaded rod 83 isconnected by a pivot pin 84. The threaded rod 83 passes upwardly throughan eye 85 in a support bracket 86 which is welded to the outer face ofthe side wall 30 of the cooling water duct 36. An abutment pad 87 isfixed to the top of the bracket 86 and the rod 83 passes upwardlythrough that pad and has screwed on to it an internally threaded bevelgear 88 which meshes with a bevel gear 89 which is fixed to the end of ahorizontally mounted rod 90 which is held in a bearing block 91 mountedon a fin 92 which is fixed by bolts 93 to a bracket 94 welded to theouter face of the hollow channel section 27. As shown in FIG. 2 each ofthe rods 90 extends alongside the channel section 27 through the tankside wall and is held in a second bearing block, not shown, in thecollar, respectively 65 and 74, and the outer end of each of the rods 90is formed as a nut for engagement by a tool for rotating the rod tocause raising or lowering of the slabs 45 about their pivots. Each ofthe gas supply ducts 60 is connected as shown at the left-hand side ofFIG. 2 to a mixer 92 which is connected by a gas supply line 93 througha flow meter 94 and an adjustable valve 95 to a line 96 which isconnected to a supply of gaseous monosilane SiH₄ in nitrogen. A secondgas supply line 97 is connected to the mixer 92 and through a flow meter98 to an adjustable valve 99 connected by a gas supply line 100 to asupply of a mixture of nitrogen and hydrogen whose composition isadjustable.

Regulation of the valves 95 and 99 permits the composition of thesilane-containing gas supplied to the ducts 60 to be regulated so thatthe gas comprises from 0.1% to 20% by volume of silane, up to 10% byvolume of hydrogen, and from 70% to 99.9% by volume of inert gas whichin this instance is nitrogen. Preferably the ducts 60 at both ends ofthe gas distributor are connected to the mixer 92 but a separate supplymay be provided for both ends of the distributor. Whilst, in theembodiment described, gas is supplied at both ends of the distributor,it may be sufficient to supply gas to the duct at one point. Valves inthe gas supply are employed to regulate the rate of flow ofsilane-containing gas into the gas supply duct 35 and thereby to controlthe flow through the waffle plate 53 into the heated chamber 40 and therate of flow of gas into the duct 35 is such as to ensure release of gasthrough the waffle plate and the aperture 43 into the chamber 40 atuniform pressure along the whole length of the chamber 40 to provideuniformity of treatment across the whole width of the ribbon.

The total flow rate of the silane-containing gas is regulated byadjustment of the valves 95 and 99 to provide a uniform coating and thecomposition of the silane-containing gas, in particular the silaneconcentration, is regulated by adjustment of the valve 95 in relation tothe speed of advance of the ribbon of glass 21 along the bath surfacebeneath the open face of the chamber 40 to maintain a rate of pyrolysisof silane on the hot glass surface 41 producing a silicon coating ofpredetermined thickness on that surface by the time the ribbon of glassemerges from beneath the open-faced chamber. Usually in carrying out theinvention the regulation of the composition of the silane-containing gasis effected in conjunction with the inspection of the product, and thesetting of the valves is preserved when the desired thickness of siliconcoating is being produced. The composition may be predetermined bycalculation and/or experiment and fine adjustment made subsequently toachieve the desired coating thickness.

Hydrogen and nitrogen of the silane-containing gas escape through thegap defined between the lower edges 54 of the open-faced chamber and theupper surface of the ribbon of glass. It is also envisaged that a sealmay be provided between the lower surface of the upstream side wall 45of the chamber by treating the slabs 45 to enable a body of moltenmaterial, for example molten tin, to cling to the lower surface of thatwall and to contact the upper surface of the ribbon of glass just beforeit is coated. The provision of such a seal ensures that all gas escapetakes place in a downstream direction for entrainment into the generalflow of protective atmosphere purging the outlet end of the bath throughthe outlet 20.

Extract ducts may be provided, for example slotted tubes attached to theoutside of the distributor to extract spent gases from the chamber 40.

Rapid heating of the silane-containing gas is desired withoutdecomposition in the gas phase and the heating of the gas as it flows inthe outlet chamber 45 is affected by the residence time of the gas inthe outlet chamber which depends on the internal volume of that chamberand its configuration.

FIGS. 7 and 8 illustrate two alternative arrangements of the outletchamber in which side walls 101 are thick carbon walls which are fixedby bolts 102 to the support plates 55. Intermediate slabs 42 of thermalinsulation are provided. The walls 101 are shaped to define a channel inthe chamber which diverges from the aperture 43 to the open face of thechamber. The inner surfaces 103 of the side walls may have a curvedshape as shown in FIG. 7 with a rapidly increasing cross-section so asto provide rapid expansion of the gases flowing downwardly through theaperture 43.

A more gentle expansion and a modified flow pattern are provided in theembodiment of FIG. 8 in which the inner faces 103 of the walls 101 arestraight sloping faces.

Another distributor according to the invention is illustrated in FIG. 9,and has an open-faced chamber shaped for laminar flow of the coating gasparallel to the glass surface 41.

The distributor comprises an inverted U-section channel member 130having side walls 131, 132 and a top wall 133. The channel within the130 member is divided into two sections by a vertical partition 134welded at 135 to the top wall 133. Horizontal members 138 and 139 extendinwardly from the side wall 131 and the partition 134 adjacent theirlower edges and together define an elongated aperture 136. A secondsmaller U-section channel member 140 is disposed symmetrically over theaperture 136, its lower edges being welded to the horizontal members 138and 139. A horizontal member 141 is welded to the base of the verticalpartition 134 and the base of the wall 132 extends beyond the wall 132.

The two inverted U-section channel members 130 and 140, together withhorizontal members 138 and 139, define a U-section duct 142 for thepassage of a cooling fluid. A rectangular return duct 143 is defined bythe side wall 132, the top wall 133, the partition 134 and thehorizontal member 141. The interior face of U-section channel member140, together with horizontal member 138 and 139, defines a gas supplyduct 144.

Gas flow restrictor means 145, similar to that shown in FIGS. 3, 4 and 5having a waffle plate 56 between support plates 55, is bolted to theunderside of horizontal members 138 and 139 by countersunk bolts 57, sothat the waffle plate 56 is aligned with aperture 136. As in theembodiment of FIG. 3, the channels in the waffle plate 56 are of smallcross-sectional area relative to the area of the gas supply duct 144.

Shaped carbon blocks 146, 147, 148 and 149 define a U-shaped chamber 150having an open face extending across the upper surface 41 of the ribbonof glass 21 to be coated. The carbon block 146 comprises upper and lowersections 152 and 153 with a layer 154 of fibrous thermal insulationbonded between them. Shaped carbon block 147 similarly comprises alaminate of upper and lower sections 155 and 156 with a layer of fibrousthermal insulation 157 bonded between them. The thermal insulationlayers 154 and 157 control the flow of heat between the cooled gassupply duct and the chamber 150, allowing the carbon shapes defining thechamber walls to heat up in use.

A plurality of spaced distance pieces 167 are welded to the outer faceof side wall 132 of the U-section channel member 130. The shaped carbonblock 148 stands on the top face of carbon block 147 in contact with therear faces of distance pieces 167. Spaced distance pieces 158,corresponding to distance pieces 167, are disposed in the downstreamlimb of the U-shaped chamber 150 and separate shaped carbon blocks 148and 149. The distance pieces 158 and the carbon block 148 are secured tothe distance pieces 167 by bolts 160 whose heads are countersunk in thedistance pieces 158. The shaped carbon block 149 is secured by bolts 168which are secured in the distance pieces 158. The bolts 168 also securebrackets 162 and 162 which extend along the distributor and support aduct 163 having an elongated aperture 164 for the supply of gas underpressure.

The faces of the carbon blocks 146, 147, 148 and 149 which define thewalls of the U-shaped chamber 150 are smooth and shaped to avoidturbulence and allow laminar flow of gas over the glass surface 41.Subsidiary carbon blocks 165 and 166 are secured to the back face ofshaped carbon block 149 at the top and bottom thereof to assist incontrolling the gas flow. The lower subsidiary block extendshorizontally close to the gas surface and restricts the flow of gasunder the foot of block 149.

In use, the ducts 142 and 143 (which are interconnected by a hole in thepartition 134 at one end thereof) are connected with a supply of coolingfluid and the gas supply duct 144 is connected to a source of silane gasin the same way as the apparatus of FIGS. 1 to 6. In addition, the duct163 is connected to a source (not shown) of gas under pressure (forexample, nitrogen/hydrogen) which flows through the apertures 164 andserves to disperse waste gas exiting from the U-shaped chamber 150.

Some examples of operation will now be described. Examples 1 to 4 relateto the production of a silicon coating on the upper surface of a ribbonof float glass shortly before the ribbon is discharged from the floatglass manufacturing apparatus. Example 5 relates to the application of asilicon coating to a ribbon of rolled plate glass as it passes throughan annealing lehr.

In the examples, the optical properties of the products are given. Thethicknesses quoted for the coatings are determined from the opticalthickness measurements in known manner. The white light transmissionsare determined using, as the light source, C.I.E. Illuminant C. Theoptical properties quoted were determined from measurements made withthe coating on the side of the glass facing the light source used.

EXAMPLE 1

Using the apparatus illustrated in FIGS. 1 to 6 a protective atmosphereconsisting of 94% by volume nitrogen and 6% by volume hydrogen ismaintained in the headspace 14 over the molten tin bath along which theribbon of float glass is advanced.

The ribbon 21 is discharged from the apparatus by the rollers 22 at aspeed of 295 meters per hour and passes through the annealing lehr whichis beyond the rollers 22.

The gas distributor is located near the outlet end of the bath where theglass surface temperature is about 610° C., and is mounted with thelower edge of the outlet chamber 45 as close as possible to the uppersurface 58 of the ribbon 21 without making actual contact.

A silane-containing gas consisting of 3.9% by volume monosilane SiH₄,93.9% nitrogen and 2.2% hydrogen was supplied to the distributor throughthe ducts 57 at a rate of 90 liters per minute per meter of length ofthe distributor. The feed rate was adjusted until a substantiallyuniform silicon coating was produced on the glass at the outlet end ofthe lehr.

The hue of the silicon-coated glass sheets cut from the ribbon of glassappeared brown by transmitted light and silver by reflected light. Thethickness, refractive index, and optical properties of the coated glassare as follows:

    ______________________________________                                        Wavelength of maximum reflection (λ max)                                                         5300A                                               Refractive index          3.73                                                Optical Thickness         1325A                                               Thickness                 355A                                                White light transmission  23%                                                 Direct solar heat transmission                                                                          34%                                                 Total heat transmission   40%                                                 Solar radiant reflection  48%                                                 ______________________________________                                    

EXAMPLE 2

The procedure of Example 1 was repeated but using apparatus modified asillustrated in FIG. 7 so that the outlet chamber 45 has a special shape.

Process conditions were as follows:

    ______________________________________                                        Composition of protective atmosphere                                                                94% by volume                                                                 nitrogen                                                Lehr speed of ribbon  215 metres/hour                                         Glass temperature     640° C.                                          Composition of gas mixture supplied                                                                 2.6% by volume                                                                mono-silane SiH.sub.4                                                         4.7% by volume                                                                hydrogen                                                                      92.7% by volume                                                               nitrogen                                                Rate of supply of gas mixture                                                                       84 litres/minute/                                                             metre of distri-                                                              butor length.                                           ______________________________________                                    

A uniform silicon coating was produced and the hue of the coated glasswas brown in transmitted light and silver in reflected light.

The thickness, refractive index, and optical properties of the coatedglass were as follows:

    ______________________________________                                        Wavelength of maximum reflection (λ max)                                                         5850A                                               Refractive index          3.55                                                Optical thickness         1463A                                               Thickness                 412A                                                White light transmission  24%                                                 Direct solar heat transmission                                                                          33%                                                 Total heat transmission   39%                                                 Solar radiant reflection  47%                                                 ______________________________________                                    

EXAMPLE 3

The procedure of Example 1 was again repeated but using a modificationof the outlet chamber as illustrated in FIG. 8. The process conditionswere as follows:

    ______________________________________                                        Composition of protective atmosphere                                                               94% by volume nitrogen                                                         6% by volume hydrogen                                   Lehr speed of ribbon 295 metres/hour                                          Glass temperature    650° C.                                           Composition of gas mixture supplied                                                                2.3% by volume mono-                                                          silane SiH.sub.4                                                              5.2% by volume hydrogen                                                       92.5% by volume                                                               nitrogen                                                 Rate of supply of gas mixture                                                                      87 litres/minute/metre                                                        of distributor length.                                   ______________________________________                                    

A uniform coating was again produced and the hue of the coated glass wasbrown in transmitted light and silver in reflected light.

The thickness, refractive index of the coating and the opticalproperties of the glass were as follows:

    ______________________________________                                        Wavelength of maximum reflection (λ max)                                                         5100A                                               Refractive index          3.60                                                Optical thickness         1275A                                               Thickness                 354A                                                White light transmission  27%                                                 Direct solar heat transmission                                                                          36%                                                 Total heat transmission   41%                                                 Solar radiant reflection  47%                                                 ______________________________________                                    

Another example of operation with the distributor of FIGS. 1 to 6 is asfollows:

EXAMPLE 4

The ribbon of glass being coated was 3 m wide.

The process conditions were as follows:

    ______________________________________                                        Composition of protective atmosphere                                                               90% by volume                                                                 nitrogen                                                                      10% by volume                                                                 hydrogen                                                 Lehr speed of ribbon 360 metres/hour                                          Glass temperature    660° C.                                           Composition of gas mixture supplied                                                                2.2% by volume mono-                                                          silane SiH.sub.4                                                              5.6% by volume                                                                hydrogen                                                                      92.2% by volume                                                               nitrogen                                                 Rate of supply of gas mixture                                                                      66 litres/minute/                                        metre of distributor                                                                               length.                                                  ______________________________________                                    

A uniform coating resulted the hue of which was brown in transmittedlight and silver in reflected light.

The thickness of the coating and optical properties of the coated glasswere as follows:

    ______________________________________                                        Wavelength of maximum reflection (λ max)                                                         4400A                                               Refractive index          2.9                                                 Optical thickness         1100A                                               Thickness                 380A                                                White light transmission  36%                                                 Direct solar heat transmission                                                                          47%                                                 Total heat transmission   54%                                                 Solar radiant reflection  35%                                                 ______________________________________                                    

EXAMPLE 5

The procedure of Example 1 was repeated using the modified apparatusillustrated in FIG. 9 and passing the silane-containing gas through theopen-faced chamber parallel to the glass surface under substantiallylaminar flow conditions. The total gas flow rate was set to provide auniform coating and the concentration of silane in the gas varied tovary the thickness of the coating whilst preserving uniformity. Theprocess conditions were:

    ______________________________________                                        Composition of protective                                                                             90% by volume nitrogen                                atmosphere              10% by volume hydrogen                                Lehr speed of ribbon    365 metres/hour                                       Glass temperature       620°C.                                         Rate of supply of gas mixture                                                                         50 litres/minute/metre                                                        of distributor length                                 Composition of gas mixture                                                                      (a)   5% by volume mono-                                    supplied                silane, SiH.sub.4                                                             95% by volume nitrogen                                                  (b)   10% by volume mono-                                                           silane, SiH.sub.4                                                             90% by volume mono-                                                           silane, SiH.sub.4                                                             90% by volume nitrogen                                                  (c)   7% by volume mono-                                                            silane44, SiH.sub.4                                                           3% by volume hydrogen                                                         90% by volume nitrogen                                ______________________________________                                    

The thickness, refractive index and optical properties of the glasswere:

    ______________________________________                                                          5(a)  5(b)    5(c)                                          ______________________________________                                        Wavelength of maximum reflection                                                                  4800A   7100A   6000A                                     (λ max)                                                                Refractive index    3.45    4.00    3.80                                      Optical thickness   1200A   1775A   1500A                                     Thickness           348A    444A    395A                                      White light transmission                                                                          25%     21%     18%                                       Direct solar heat transmission                                                                    37%     24%     28%                                       Total heat transmission                                                                           43%     31%     34%                                       Solar radiant reflection                                                                          43%     54%     52%                                       Colour in transmission                                                                            brown   green   brown                                     Colour in reflection                                                                              silver  gold    silver/                                                                       gold                                      ______________________________________                                    

As well as application of the invention to the coating of float glassduring its manufacture, the method of the invention can also be employedfor coating a hot ribbon of glass produced in other ways, for example bythe known rolling process or vertical drawing process in which a formedribbon of glass is advanced through an annealing lehr. One form of gasdistributor for coating a rolled ribbon of glass in an annealing lehr isillustrated diagrammatically in FIG. 10. This gas distributor would belocated in the lehr where the glass temperature is in the range 400° C.to 750° C. The ribbon of rolled plate glass 110 is advancing on lehrrollers indicated at 111. The gas distributor includes a hood 112 whichis connected to an extract duct 113. The gas distributor is locatedunder the extraction hood and the side walls of the extraction hood 112extend downwardly close to the upper surface of the ribbon of glass 110.The gas distributor comprises a protective hood 114 in which there isdefined the gas supply duct 35 surrounded by a water cooled jacket 36 insimilar manner to the embodiment illustrated in FIG. 3.

Gas-flow restrictor means in the form of a waffle plate 56 made up ofcrimped metal sheets of the same kind as illustrated in FIG. 5. Thewaffle plate 56 is carried by support plates 55.

The elongate open-faced chamber 40 is defined beneath the waffle plateby carbon side pieces which are L-shaped to define an aperture in theroof of the chamber beneath the gas flow restricting waffle plate 56.The bottom of the side walls of the carbon shapes extend close to theupper surface of the ribbon of glass and this arrangement providesrelease of silane-containing gas into the chamber 40 at constantpressure along the length of the chamber which extends across the widthof the advancing ribbon of rolled glass. In order to provide anon-oxidising atmosphere beneath the protective hood 114, protectiveatmosphere, for example a nitrogen atmosphere or an atmosphereconsisting of 95% by volume nitrogen and 5% by volume hydrogen, isintroduced through ducts 117 which are defined at the top of the hood114 upstream and downstream of the gas distributor. Gas flow restrictingmeans in the form of waffle plates 118 similar to the waffle plate 56provide an outlet from each of the ducts 117 for protective atmosphereto flow downwardly at substantially constant pressure across the wholewidth of the distributor toward the upper surface of the ribbon ofglass. In this way there is a constant flow of protective atmosphere inthe region between the carbon side pieces 115 and the protective hood.Gases are extracted beneath the bottom edges of the protective hoodupwardly through the extraction hood 112 to the extraction duct 113. Inthis way a non-oxidising atmosphere is provided in the region of thelehr where the silane coating is being produced on the upper surface ofthe ribbon of glass and there is continuous extraction of waste gasesaway from the coating zone thereby avoiding the possibility ofsilane-containing gases diffusing along the whole length of theannealing lehr.

A modification of the apparatus of FIG. 10 may also be used in anenviroment where there is no protective atmosphere, such as an annealinglehr, and without a protective atmosphere being supplied directly to thecoating station. In this modification the ducts 117 and waffle plates118 are omitted and the bottom of each of the carbon side pieces 115 iswidened in the direction of glass advance to a dimension whichsubstantially inhibits ingress of external atmosphere into the chamber40.

An example of operation of this modified apparatus for coating rolled,patterned glass as it passes through an annealing lehr is as follows:

EXAMPLE 6

    ______________________________________                                        Coated width of ribbon                                                                            1 metre                                                   Lehr Speed of Ribbon                                                                              350 metres/hour                                           Glass temperature   620° C.                                            Composition of gas mixture supplied                                                               5.0% by volume monosilane                                                     SiH.sub.4                                                                     5.0% by volume hydrogen                                                       90.0% by volume nitrogen                                  Rate of supply of gas mixture                                                                     60 Litres/minute/metre of                                                     distributor length.                                       ______________________________________                                    

A uniform coating was produced which was brown in transmitted light, andsilver in reflected light.

The optical properties of the coating are as follows:

    ______________________________________                                        Wavelength of maximum reflection (λ max)                                                         4000A                                               Refractive index          3.2                                                 Optical thickness         1000A                                               Thickness                  312A                                               White light transmission  33%                                                 Direct solar heat transmission                                                                          45%                                                 Total heat transmission   51%                                                 Solar radiant reflection  36%                                                 ______________________________________                                    

Also float glass may be coated in the annealing lehr through which theribbon of float glass is advanced after it has been discharged from thebath, as long as the gas distributor is located in the lehr where thetemperature of the glass is above 400° C.

The silicon-coated glass produced, when cut into sheets from the ribbonin conventional manner, had a pleasing appearance and useful solarcontrol properties making it useful for glazing units especially forwindows in buildings.

FIG. 11 illustrates such a glazing unit according to the inventioncomprising a sheet of glass 120 having a coating of silicon 121, thethickness of which is greatly exaggerated for the sake of clarity. Thesheet is mounted in a frame 122 which is fixed in a wall 123 in anyconventional manner.

The silicon-coated glass may also be used in multiple-glazing units,especially double-glazing units. One such unit is illustrated in FIG. 12and comprises a sheet of uncoated glass 126 and a sheet of glass 120having a silicon coating 121 which, in the embodiment illustrated, isdisposed internally of the unit to protect it from weathering. Thesheets of glass are spaced apart by spacer elements 124 of conventionalkind, the surfaces of the glass adhering to the spacer elements 124using a suitable adhesive. The whole unit is mounted in a frame 125 forfixing into a wall in conventional manner.

The placing of the silicon coated faces of the glass internally of thedouble glazing unit protects the silicon coatings from weathering. Inview of the durability of the silicon coatings however this may not benecessary and the silicon-coated surfaces of the glass sheet may beoutside surfaces.

A coated glass sheet may constitute the inner or the outer pane of adouble-glazing unit. In a multiple glazing unit comprising three or morepanes the coated glass may be used as an intermediate pane or as theinner or outer pane.

For some applications where high strength glass is required it isdesirable to toughen the glass by a thermal tempering process and thesilicon coated glass of the invention has been thermally toughened byconventional procedures without any significant deterioration of thesilicon coating. Also the coated glass can be laminated.

The pleasing appearance of the silicon coated glass also providesapplications in which its solar control properties are not required, forexample in interior glazing, or as a decorative and sometimes structuralelement in furniture. Thus for example the coated glass may constitute atable top.

The silicon coated glass may also be used as a mirror by providing adark background to prevent light transmission through the glass, such amirror comprising silicon-coated glass according to the invention havinga dark coating, for example black paint, either on top of the siliconcoating or on the opposite face of the glass.

In carrying out the invention other silanes may be employed as aconstituent of the silane-containing gas, for example disilane Si₂ H₆ ordichlorosilane SiH₂ Cl₂.

The method of the invention has been used to form a silicon coating onflat glass having a thickness in the range 200A to 1,000A or more.Preferably the coatings are of thickness in the range 250A to 600A.

Thinner coatings within this range are silvery blue in reflected lightand brown in transmitted light. As the thickness of the coatingincreases so there is a gradual change in its appearance so that whenthe thickness is about 400A the coated glass appears yellow-silver inreflected light and brown in transmitted light.

The transmission and reflection colours continue to deepen until thethickness reaches about 450A at which thickness interference coloursbecome significant. Interference colours are not usually desirable onfloat glass, although they can impart attractive effects to patternedglass. Generally, for solar control, coatings on non-patterned glass arepreferred having a thickness in the range 300A to 450A, coatings ofuniform appearance being readily achieved within this range.

The thickness of the coating on the glass has been determined by asimple optical technique, by measuring the wavelength (λ max) at whichlight reflection from the coating is a maximum (R max). Thin film theoryshows: ##EQU1## where Nc = refractive index of the coating

Ng = refractive index of the glass

Thus, provided the refractive index of the glass is known, therefractive index may be determined. The refractive index is related tothe thickness of the coating by the equation ##EQU2## where d isthickness of the coating.

We claim:
 1. A glazing unit having desirable solar control propertiescomprising a sheet of silicon coated flat glass having a substantiallyuniform silicon coating of optical thickness in the range 950A to 1600Aand a refractive index in the range 3.0 to 4.0 and capable oftransmitting light.
 2. A glazing unit according to claim 1 having, whenviewed from the coated side, a white light transmission in the range 17%to 34%, a direct solar heat transmission in the range 27% to 45% and asolar radiant reflection in the range 34% to 52%.
 3. A glazing unithaving desirable solar control properties comprising a sheet of glasshaving a coating of thickness in the range of 250 to 600A and consistingessentially of silicon on a major face thereof and a frame for thatsheet, said glazing unit being glazed in the opening of a wall of abuilding to provide a window in said wall.
 4. The glazing unit of claim3 wherein the coating has a thickness in the range of 300A to 450A.
 5. Amultiple glazing unit having desirable solar control propertiescomprising at least two sheets of glass spaced apart by spacer elements,at least one of said sheets having a coating of thickness in the rangeof 250 to 600A and consisting essentially of silicon on a major surfacethereof.
 6. The multiple glazing unit of claim 5 wherein the coating hasa thickness in the range of 300A to 450A.
 7. A multiple glazing unitaccording to claim 5 wherein the silicon coated surface of said at leastone of said sheets is disposed internally of the unit and is therebyprotected.
 8. A multiple glazing unit according to claim 5 wherein saidat least one of said sheets has, when viewed from the coated side, awhite light transmission in the range 17% to 34%, a direct solar heattransmission in the range 27% to 45% and a solar radiant reflection inthe range 34% to 52%.
 9. The multiple glazing unit of claim 8 whereinthe coated has a thickness in the range of 300A to 450A.
 10. A multipleglazing unit according to claim 6 wherein the silicon coated surface ofsaid at least one of said sheets is disposed internally of the unit andis thereby protected.
 11. A multiple glazing unit having desirable solarcontrol properties comprising at least two sheets of glass spaced apartby spacer elements, at least one of sheets having a coating of thicknessin the range of 250 to 600A and consisting essentially of silicon on amajor surface thereof disposed internally of the unit, said at least onesheet, when viewed from the coated side, having a white lighttransmission in the range 17% to 34%, a direct solar heat transmissionin the range 27% to 45%, and a solar radiant reflection in the range 34%to 52%.
 12. The multiple glazing unit of claim 11 wherein the coatinghas a thickness in the range of 300A to 450A.
 13. The multiple glazingunit of claim 11 glazed in the opening of a wall of a building toprovide a window in said wall.
 14. The multiple glazing unit of claim 13wherein the coating has a thickness in the range of 300A to 450A.
 15. Aglazing unit having desirable solar control properties glazed in theopening of a wall of a building to provide a window and comprising asheet of glass having a coating consisting essentially of silicon on amajor face thereof, which coating has a thickness in the range of 250Ato 600A.
 16. The glazing unit of claim 15 wherein the coating has athickness in the range of 300A to 450A.